feat(channel): 缓存扁平化 + 网关映射集成 + 计费模式统一 + 模型限制

- 缓存重构为 O(1) 哈希结构 (pricingByGroupModel, mappingByGroupModel)
- 渠道模型映射接入网关流程 (Forward 前应用, a→b→c 映射链)
- 新增 billing_model_source 配置 (请求模型/最终模型计费)
- usage_logs 新增 channel_id, model_mapping_chain, billing_tier 字段
- 每种计费模式统一支持默认价格 + 区间定价
- 渠道模型限制开关 (restrict_models)
- 分组按平台分类展示 + 彩色图标
- 必填字段红色星号 + 模型映射 UI
- 去除模型通配符支持

frontend/src/api/admin/channels.ts

@@ -29,6 +29,7 @@ export interface ChannelModelPricing {
   cache_write_price: number | null
   cache_read_price: number | null
   image_output_price: number | null
+  per_request_price: number | null
   intervals: PricingInterval[]
 }
 
@@ -37,8 +38,11 @@ export interface Channel {
   name: string
   description: string
   status: string
+  billing_model_source: string // "requested" | "upstream"
+  restrict_models: boolean
   group_ids: number[]
   model_pricing: ChannelModelPricing[]
+  model_mapping: Record<string, string>
   created_at: string
   updated_at: string
 }
@@ -48,6 +52,9 @@ export interface CreateChannelRequest {
   description?: string
   group_ids?: number[]
   model_pricing?: ChannelModelPricing[]
+  model_mapping?: Record<string, string>
+  billing_model_source?: string
+  restrict_models?: boolean
 }
 
 export interface UpdateChannelRequest {
@@ -56,6 +63,9 @@ export interface UpdateChannelRequest {
   status?: string
   group_ids?: number[]
   model_pricing?: ChannelModelPricing[]
+  model_mapping?: Record<string, string>
+  billing_model_source?: string
+  restrict_models?: boolean
 }
 
 interface PaginatedResponse<T> {